1. Field of the Invention
The invention concerns a medical tool, in particular a vertebral distractor, of the type according to the precharacterizing portion of patent claim 1.
2. Description of the Related Art
Distractors are employed in surgery, where it is necessary to change the separation between two parts of the spinal parts, in particular, to increase the separation. A vertebral distractor has the task of increasing the separation of two vertebrae, in particular during an operational procedure in the area of the vertebral disks. A distractor is essentially comprised of two pliers-shaped link elements, with grip parts and with engagement parts in the form of jaws. If the engagement parts can be changed out, they are referred to as “valves”. The valves are in operating engagement with the grip elements. For spreading apart two vertebra of the spinal column, the distractor with the two valves is introduced between the vertebra to be spread apart. Spreading occurs by operation of the grip elements. The degree of spreading between the valves can be set by an adjustment element.
U.S. Pat. No. 6,017,342 discloses vertebral distractors comprised of two link parts. Each link part includes a grip element as well as a jaw. The two link parts are connected rotatably in the area between the grip parts and the jaws. According to this reference, the degree of opening of the two jaws is fixed using an adjustment screw, which is connected with the linkage parts in the area of the grip elements via a linkage mechanism.
U.S. Pat. No. 2002,0,019,637 A1 discloses a distractor with fold-back grip elements. Thereby it becomes possible, after a successful spreading of two vertebra, to fold the projecting grip elements, which essentially interfere with the operation, back along the plane of the body to be operated upon.
Also known in the art are vertebral distractors with exchangeable jaws. The valves are either connected with the pliers' elements associated with the linkage part via a screw connection, or however are secured on the pliers element via a detent or locking mechanism. In the first case, in order to change the valves, the screw connection must be undone using a tool. In the second case also a tool is necessary for releasing the locking connection. Accordingly it can be seen that a change-out of the valves of a distractor during a surgical intervention is almost impossible, whereby the multi-facetted usefulness of the tool is substantially reduced. Vertebral distractors with the above-described blocking mechanism are shown on the home page of Fa. Beere Medical Precision Instruments at the site www.beeremedical.com/pages/comdist.htm. Further, in the case of vertebral distractors with change out valves, there is the requirement that the forces exerted upon the pliers elements via the valves must be transmitted without free play.